diff --git a/.gitignore b/.gitignore
index 473ae13aa..cfcee7150 100644
--- a/.gitignore
+++ b/.gitignore
@@ -38,8 +38,8 @@
 /base
 /build
 /buildtools
-/chromium/.gclient.bot
-/chromium/.gclient_entries
+/chromium/.gclient.tmp
+/chromium/.gclient.tmp_entries
 /chromium/.last_sync_chromium
 /chromium/src
 /google_apis
diff --git a/sync_chromium.py b/sync_chromium.py
index afcc281b4..9d2c05b9d 100755
--- a/sync_chromium.py
+++ b/sync_chromium.py
@@ -7,6 +7,21 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Script to download a Chromium checkout into the workspace.
+
+The script downloads a full Chromium Git clone and its DEPS.
+
+The following environment variable can be used to alter the behavior:
+* CHROMIUM_NO_HISTORY - If set to 1, a Git checkout with no history will be
+  downloaded. This is consumes less bandwidth and disk space but is known to be
+  slower in general if you have a high-speed connection.
+
+After a successful sync has completed, a .last_sync_chromium file is written to
+the chromium directory. While it exists, no more gclient sync operations will be
+performed until the --target-revision changes or the SCRIPT_VERSION constant is
+incremented. The file can be removed manually to force a new sync.
+"""
+
 import argparse
 import os
 import subprocess
@@ -14,20 +29,28 @@ import sys
 
 # Bump this whenever the algorithm changes and you need bots/devs to re-sync,
 # ignoring the .last_sync_chromium file
-SCRIPT_VERSION = 2
+SCRIPT_VERSION = 3
 
 ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
+CHROMIUM_NO_HISTORY = 'CHROMIUM_NO_HISTORY'
+
+def _parse_gclient_dict():
+  gclient_dict = {}
+  try:
+    main_gclient = os.path.join(os.path.dirname(ROOT_DIR), '.gclient')
+    with open(main_gclient, 'rb') as deps_content:
+      exec(deps_content, gclient_dict)
+  except Exception as e:
+    print >> sys.stderr, 'error while parsing .gclient:', e
+  return gclient_dict
+
+
+def get_cache_dir():
+  return _parse_gclient_dict().get('cache_dir')
 
 
 def get_target_os_list():
-  try:
-    main_gclient = os.path.join(os.path.dirname(ROOT_DIR), '.gclient')
-    config_dict = {}
-    with open(main_gclient, 'rb') as deps_content:
-      exec(deps_content, config_dict)
-    return ','.join(config_dict.get('target_os', []))
-  except Exception as e:
-    print >> sys.stderr, "error while parsing .gclient:", e
+  return ','.join(_parse_gclient_dict().get('target_os', []))
 
 
 def main():
@@ -55,7 +78,7 @@ def main():
   if os.path.exists(flag_file):
     with open(flag_file, 'r') as f:
       if f.read() == flag_file_content:
-        print "Chromium already up to date:", opts.target_revision
+        print 'Chromium already up to date: ', opts.target_revision
         return 0
     os.unlink(flag_file)
 
@@ -67,6 +90,7 @@ def main():
   ]
 
   if os.environ.get('CHROME_HEADLESS') == '1':
+    # Running on a buildbot.
     args.append('-vvv')
 
     if sys.platform.startswith('win'):
@@ -74,23 +98,37 @@ def main():
                                 'b', 'git-cache')
     else:
       cache_path = '/b/git-cache'
+  else:
+    # Support developers setting the cache_dir in .gclient.
+    cache_path = get_cache_dir()
 
+  # Allow for users with poor internet connections to download a Git clone
+  # without history (saves several gigs but is generally slower and doesn't work
+  # with the Git cache).
+  if os.environ.get(CHROMIUM_NO_HISTORY) == '1':
+    if cache_path:
+      print >> sys.stderr, (
+          'You cannot use "no-history" mode for syncing Chrome (i.e. set the '
+          '%s environment variable to 1) when you have cache_dir configured in '
+          'your .gclient.' % CHROMIUM_NO_HISTORY)
+      return 1
+    args.append('--no-history')
+    gclient_entries_file = os.path.join(opts.chromium_dir, '.gclient_entries')
+  else:
+    # Write a temporary .gclient file that has the cache_dir variable added.
     gclientfile = os.path.join(opts.chromium_dir, '.gclient')
     with open(gclientfile, 'rb') as spec:
       spec = spec.read().splitlines()
       spec[-1] = 'cache_dir = %r' % (cache_path,)
-    with open(gclientfile + '.bot', 'wb') as f:
+    with open(gclientfile + '.tmp', 'wb') as f:
       f.write('\n'.join(spec))
 
     args += [
-      '--gclientfile', '.gclient.bot',
+      '--gclientfile', '.gclient.tmp',
       '--delete_unversioned_trees', '--reset', '--upstream'
     ]
     gclient_entries_file = os.path.join(opts.chromium_dir,
-                                        '.gclient.bot_entries')
-  else:
-    args.append('--no-history')
-    gclient_entries_file = os.path.join(opts.chromium_dir, '.gclient_entries')
+                                        '.gclient.tmp_entries')
 
   # To avoid gclient sync problems when DEPS entries have been removed we must
   # wipe the gclient's entries file that contains cached URLs for all DEPS.